Hydrocarbyl bisphosphate compounds of the general formula ##STR1## where R and R' are the same or different and are hydrocarbyl groups which are either substituted with non-interfering substituents or are unsubstituted are a known class of flame retardant additive. Some examples of groups which form the basis for such groups are alkyl(ene) and aryl(ene). Representative substituents include alkyl.
U.S. Pat. No. 4,134,876, British Patent No. 2,061,949, and Japanese Patent Publication No. 227,632/1988 which all relate to compounds of this general type teach that they may be formed by first reacting POCl.sub.3 with a diol containing the group desired for R to form a product which is then reacted with an alcohol containing the desired group R'. Unfortunately, when such a reaction is performed, an undesired amount of oligomeric product is commonly formed in the first reaction of diol and POCl.sub.3.
U.S. Pat. No. 3,254,973 illustrates reaction of phosphorus oxychloride and ortho-cresol to form di-o-tolyl phosphorochloridate which is then reacted with bisphenol A. No discussion is contained in this reference regarding the formation of undesired oligomeric products or of triphenyl phosphate. Also, this patent indicates that the reaction mixture from the initial reaction of phosphorus oxychloride and o-cresol is distilled through a packed column to isolate various cuts of di-o-tolyl phosphorochloridate. Those cuts distilling at 182.degree.-187.degree. C. were combined for later use as a reagent for reaction with bisphenol A to form the desired bisphosphate end-product. The need for distillation in the process shown in this patent has certain disadvantages. First, the presence of the distillation step makes the overall process more complicated and expensive than an analogous process not containing the need for distillation of product di-o-tolyl phosphorochloridate in view of both the presence of the step itself as well as the need for the equipment for distillation (distillation column and collection vessel). Second, since the product which is distilled is corrosive, the extra distillation equipment needed must have appropriate materials of construction which can also raise the expense of the overall process.